Loud speaker



Aug. 2, 1932. CHANN 1,869,665

LQUD SPEAKER Filed March 14. 1950 INVENTOR Thomas C/mnn ATTORNE;

Patented Aug. 2, 1932 UNITED srrss THOMAS CHANN', or NEW YOTBK, n. Y.

LOUD SPEAKER Application filed March 14, 1930. Serial No. 435,913.

This invention relates to electrically operated sound reproducers suchas used in radio receiving apparatus, electric phonographs, and thelike, and more particularly 5 to such sound reproducing apparatus inwhich there is utilized a direct acting diaphragm or sounding boardutilizing the socalled dynamic or moving coil drive.

It is an object of this invention to provide 1 a sound reproducer of theclass described which is so arranged as to respond to electricalcurrents having a frequency as low as, or lower than, the lower limit ofaudibility and as high as, or higher than, the upper 1 limit ofaudibility.

It is a further object of the invention to provide a sound reproducer ofthe class described which is capable of delivering sound H correspondingfaithfully to the electric our- 29 rents of sound frequency which areutilized for its operation.

It is a further object of this invention to provide a sound reproducerof the class described having its voice coil so mounted as to beextremely free to move in an axial direction, and substantiallyimmovable in a direc tion transverse to its normal motion. I

It is a further object of the invention to provide a direct-acting loudspeaker of the class described capable of delivering sound of highquality and substantial volume and which at the same time may be simplyand economically constructed. H

Still other objects and advantages of my invention will be apparent fromthe specification.

' The features of novelty of my invention are set forth withparticularity in the appended claims. My invention itself, however, bothas to its fundamental principles, and as to its particularembodimentswill best be under-- stood by reference to the specificationand accompanying drawing, in which a Fig. 1 is an elevation view of acompleted 5 loud speaker accordlng'to my invention, part- 1y broken awayto show certain features of its interior construction, and

Fig. 2 is a plan view of the voice coil suspension.

Referring more particularly to Fig. 1

there is provided a pot which may, for example, be of conventionalconstruction utilizing a cylindrical inner pole piece 1, a cup likeshell 2, and an outer pole piece 3 secured to the shell 2 in goodmagnetic contact therewith and forming with the center pole piece anannular cylindrical air gap 4:. A unidirectional constant flux ismaintained across the air gap 4 by any suitable means as, for example,by means of the magnetizing coil 5, surrounding the center pole piece 1.The voice coil 7 is wound upon a suitable form 6 which is preferably acylinder of suitable material such as fibre, impregnated cardboard, orthe like. While other materials 85 than those mentioned may be used, ifdesired, it is preferable that the form 6 be made of nonconductingmaterial and be relatively light and rigid.

The diaphragm or sounding board itself is shown as a dish shaped member9 which is preferably given some curvature. In general I prefer to curvethe diaphragm so that a section through its center is a parabola. orapproaches a parabola. but it will be understood that while I believesuch an arrangement improves the performance of the loud speaker. it isnot essential. and other forms of diaphragms or sounding boards may beused as, for example, a cone. The diaphragm or sounding boardmay be madeof any suit able material but should be made as light as possible.Paper, impregnated fabric or the like may be used, for example, and itwill be understood that other suitable materials may also be utilized ifdesired. The size of the diaphragm. as will be understood, may be variedto suit the conditions of its use but in general it will preferably befrom six to twelve inches in diameter if it is to be used without ahorn.

. The diaphragm is preferably molded or pressed over a form intothe'desired shape and it is to be noted that instead of leaving anopening at the center as is usual in pres ent-day construction. thediaphragm is closed at the center and carries out the shape of thediaphragm to provide a continuous sound generating surface. within itsperiphery. The center part of the diaphragm is secured to the form 6 onwhich the voice coil is carried as, for example, by leaving small tabs15 at the outer end of the form 6 which may be bent outward and cementedto the diaphragm. Since the form 6 and the inner face of the diaphragm 9form in effect a closed cup extending over the center pole piece 1, itis desirable to provide means for preventing the trapping of air betweenthe center of the diaphragm and the pole piece 1 which would.

tend to damp the diaphragm, particularly at low frequencies. For thisreason, there are provided a number of openings or perforations 8 nearthe outer edge of the form 6, thus permitting the air to flow in and outof the space between the pole piece 1 and diaphragm 9 as the diaphragmmoves backward and forward.

The outer edge or rim of the diaphragm is provided with a flexiblesuspension 10 such as soft kid, silk or the like, so as not to impedethe motion of the diaphragm. The outer edge of the rim or suspension 10is clamped between clamping rings 12 and 13, the clamping ring 12 beingpreferably secured to the face of the pot by means of brackets 11, theinner ends of which may be 1Zecured to the face of the pot as by meansof olts.

Since the rim suspension 10 is made soft and freely flexible, the voicecoil and its supporting form 6 derive substantially no support from therim and therefore must be supported by additional means in order tomaintain the voice coil properly centered within'the gap. For thispurpose I provide a suspension which is extremely flexible in thedirection of movement of the voice coil while substantially preventingmovement in any other direction. This suspension 14 comprises an outerring 20, which may be clamped to the outer face of the outer pole piece.Extending inwardly from the outer ring 20, there is provided a series ofstrips 25, 26, 27, 28, 29 and 30 which strips terminate in an inner ring19. Extending inwardly from the ring 19 there are provided a pair ofstrips 28 and 24 preferably diametrically opposite each other and whichterminate in still another ring 18. Extending inwardly from the ring18-there are provided a pair of strips 21 and 22 preferablydiametrically opposite each other and also preferably disposed at rightangles to the line of the strips 23 and 24. These strips terminate in afinal inner ring 17 which engages the voice coil form 6 and is securedthereto in anysuitable way as, for example, by the provision of tabs17a, which may be bent against the voice coil form and secured thereto,In general it maybe stated that the suspension 14 is progressivelystiffer outwardly and to obtain this result the strips 23 and 24 may bemade somewhat longerthan the strips 25 and 30.-inclusive, and strips 21and 22 may be made somewhat longer than strips 23 and 24. Also ifdesired the width of the supporting strips and rings may be diminishedtoward the center, that is to say, the strips 21 and 22 and ring 18 maybe narrower than strips 23 and 24 and ring 19.

The suspension 14 is preferably made as a single stamping or punchingfrom suitable material such as thin fibre, stiff impregnated fabric orthe like, having a certain amount ofresiliency and flexibility. Thestamping is preferably slightly flexed outwardly so that in the neutralposition the center of the voice coil is slightly displaced on the outerpole piece 3 and in a direction toward the diaphragm as shown in Fig. 1.By this construction voice currents flowing through the voice coil willtend to move the coil from its neutral position outwardly to a greaterextent than inwardly. The damping effect is governed by the stiffness ofthe material used for the suspension and the spacing of rings 18 and 19.

The suspension also acts as a restoring force to bring the voice coilback to its neutral position. Both the damping and restoring forces aremade very small by making the suspension of as large a diameter and asthin as possible and it will be noted that in the preferred formillustrated in the drawing the suspension is substantially the samediameter as the diaphragm itself.

I have found that it is possible with loud speakers constructedaccording to this specification, to obtain amplitudes of movements of asmuch as one inch at frequencies of 10 cycles or lower.

While I have shown and described certain preferred embodiments in myinvention, it will be understood that modifications and changes may bemade without departing from the spirit and scope thereof, as will beunderstood by those skilled in the art and that therefore I do notdesire nor intend to limit myself to the precise arrangements shown anddescribed since the same are given by way of example and not inlimitation. Also, while I have shown and described my invention asapplied in a loud speaker, it will be understood that it is inherentlyreversiblein its action and may be utilized as a microphone, or pick-upif desired for converting sounds into electric currents correspondingthereto.

1 claim:

1. An acoustic device comprising, in combination, a convex diaphragmhaving a continuous sound generating surface at all points within itsperiphery, a cylinder secured to the center of said diaphragm on theconvex side thereof, a voice coil on said cylinder, and a flexiblesuspension surrounding said cylinder and secured thereto, and secured atits periphery to a support, said suspension being progressively stifferoutwardly.

2. An acoustic device comprising, in combination, a convex diaphragm, acylinder secured to said diaphragm on the convex side thereof, a voicecoil on said cylinder, and a flexible suspension surrounding saidcylinder and secured thereto, and secured at its periphery to a support,said suspension being in the form of a multiplicity of concentric ringshaving radial connecting strips, and said strips being ofiset outwardly.

3. An acoustic device comprising, in combination, a convex diaphragm, acylinder secured to said diaphragm on the convex side thereof, a voicecoil on said cylinder, and a flexible suspension surrounding saidcylinder and secured thereto, and secured at its periphery to a support,said suspension being flexed toward said diaphragm.

4:. An acoustic device comprising, in combination, a convex diaphragm, acylinder secured to said diaphragm on the convex side thereof, a voicecoil on said cylinder, and a flexible suspension surrounding saidcylinder and secured thereto, and secured at its periphery to a support,said suspension having a stiffness progressively increasing outwardly.

5. An acoustic device comprising, in combination, a convex diaphragm, acylinder secured to the convex side thereof, a voice coil on saidcylinder, and a flexible suspension surrounding said cylinder andsecured thereto and secured at its periphery to a support, saidsuspension being progressively stifi'er outwardly, and being flexedtoward said diaphragm.

6. An acoustic device comprising, in combination, a convex diaphragm, acylinder secured to the convex side thereof, a voice coil on saidcylinder, and a flexible suspension surrounding said cylinder andsecured thereto, and secured at its periphery to a support, saidsuspension being in the form of concentric rings interconnected by webs,and the stiffness of said suspension increasing outwardly.

Signed at New York, in the county of New York and State of New York.

THOMAS CHANN.

